Oxy Radical-Initiated Protein S-Thiolation and Enzymic Dethiolation

Abstract

It has often been suggested that protein S-thiolation/dethiolation (Figure 1) is an important form of metabolic regulation 1,2 . This suggestion usually arises from experiments in which a thiol-disulfide exchange mechanism is considered to be the basis for this process. Since cellular glutathione is normally very reduced, the thiol-disulfide exchange mechanism requires a significant oxidation of this thiol to account for appreciable protein modification in vivo. In addition, both S-thiolation and dethiolation by thiol-disulfide exchange probably require catalysis to occur at significant rates in vivo. These considerations make thiol-disulfide exchange less appealing than a direct oxy radical-initiated mechanism of S-thiolation. This paper describes experiments with electrofocusing technology to assess various mechanisms of protein S-thiolation and dethiolation.